The present invention relates to a colored glass in yellow to orange color used for a lamp or a cover for lighting, particularly for a turn signal lamp and a cover for fog lamps of automobiles, a colored glass bulb produced with said colored glass, and a method for producing the colored glass bulb.
Presently, a colored glass in yellow to orange color being used in an industrial scale is generally a glass produced by adding CdS (cadmium sulfide) or CdSe (cadmium selenide) as a colorant into R′2O—RO—SiO2 glass, wherein R′ is an alkali metal and R is an alkaline earth metal. Usually, colored glass for lamps and covers for lighting includes the colored glass produced as described above.
Also, a colored glass for lamps and covers for lighting is obtained by applying a coating with yellow to orange color on a surface of a clear glass. In this case, PbO—B2O3—SiO2 glass is added with Cr2O3 (chromium sesquioxide) or K2CrO4 (potassium chromate), and used as a coating agent of a glass having a low melting point colored with PbCrO4 (lead chromate). Also, silicone is added with a pigment of CdS, CdSe, PbCrO4, etc., or with Fe2O3 (ferric oxide) and an organic pigment etc., and used as cotaing agent.
Use of colorants and pigments such as CdS, CdSe, PbCrO4, etc. added to glasses and coating agents as described above are legally prohibited in many countries due to their extremely strong toxicity.
Organic coating agents containing, for example, silicone as described above have weak cohesion strength to glasses, and the coating with such organic coating agent tends to be easily exfoliated. Also such coating has problem in the thermal resistance, namely temperature limitation in the use, as a result of the loss of color or cracking of the coating occurs in some case.